Flame and carbon monoxide sensor and alarm circuit

ABSTRACT

A gas burner monitor providing a high level of protection by virtue of its dual sensing features wherein both flame color and combustion products are monitored by means of a simple and inexpensive electronic circuit.

United States Patent Teeters 1 Sept. 30, 1975 [54] FLAME AND CARBONIVIONOXIDE SENSOR 3.421.156 1/1969 Rowell 317/130 X AND ALARM CIRCUIT{761 lnventor: Lloyd L. Teeters, 17834 N. 18th Dr., Phoenix Ariz. 85023[22] Filed: Apr. 29. 1974 [21] Appl. No: 465,371

[52] [1.5. CI 340/237 R; 250/554; 340/227 R [51] Int. Cl. ..G08B 17/10[58] Field of Search 340/237 R, 237 S 227 R; 356/195; 250/554; 328/6;307/311; 431/13-17, 79; 317/130 [56] References Cited UNITED STATESPATENTS 3.233.595 5/1973 Benedict 340/237 R 2/1970 Wilson et al. 340/237R Primary lf.\'amim'r.l0hn W. Caldwell Assistant E.\z1minerDuniel MyerAttorney, Agent, or FirmWarren F. B. Lindsley [57] ABSTRACT A gas burnermonitor providing a high level of protection by virtue of its dualsensing features wherein both flame color and combustion products aremonitored by means of a simple and inexpensive electronic circuit.

5 Claims, 3 Drawing Figures FLAME COLOR SENSITIVE US. Patent Sept.30,1975 Sheet 1 of2 3,909,816

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FLAME AND CARBON MONOXIDE SENSOR AND ALARM CIRCUIT BACKGROUND OF THEINVENTION The number of deaths and the dollar value of property lossresulting from faulty gas-burner operation is alarmingly high. In mostcases, the water heater or furnace has been protected by means of abi-metal cut-off valve which normally shuts off the gas supply if theflame is extinguished. Nevertheless, the cut-off valve may fail tofunction properly when the flame is extinguished, in which case the gascontinues to flow into the building until an occupant is overcome oruntil an explosion or fire occurs. Furthermore, such bi-metal cut-offvalves are not effective in protecting against the improper combustionof the gas due to faulty burner operation or an inadequate supply ofair, and the resulting generation of carbon monoxide constitutes anequally hazardous and potent threat to life.

Elaborate means have been provided for the protection of suchoccurences. Light and heat-sensitive de vices are widely used inindustry to detect fires and to turn on sprinkling systems to quench thefire. Gas sensors have also been developed to detect the presence ofdangerous gases and to initiate the operation of automatic equipmentwhich terminates the supply of gas.

Unfortunately, such equipment is too expensive to be utilized in thetypical family dwelling, especially in the case of less well-to-dofamilies and in temporary or vacation homes where the majority of suchtragedies occur as the result of defective gas-burning equipment orbecause of improper installations.

What is needed is a simple and inexpensive device which is capable ofdetecting such malfunctions and which can respond by sounding an alarmor by initiating the automatic cutoff of the gas supply.

DISCUSSION OF THE PRIOR ART In US. Pat. No. 3,750,161 an electronicdetection circuit senses the presence of flames and reacts by cuttingoff the fuel supply and initiating the operation of a sprinkling systemto extinguish the fire. The fire detector and extinguisher systemdescribed in this patent does not, however, take action until a fire hasoccured and it is not effective against the presence of dangerous gasesor in the detection of faulty burner operation.

SUMMARY OF THE INVENTION The present invention comprises an extremelysimple and inexpensive electronic circuit which overcomes thedisadvantages of the prior art. The circuit incorporates a photo sensorand a carbon monoxide detector which permits the reliable detection offaulty burner operation and the sounding of an alarm before a fire, anexplosion or physical harm can occur.

It is, therefore, an object of this invention to provide an improvedmeans of protection against fire or asphyxiation resulting from impropergas burner operation.

Another object of this invention is to provide as a feature of suchprotective means a capability of sensing a faulty operation of theburner through the detection of improper flame color.

A further object of this invention is to provide as another feature ofsuch protective means a capability to sense improper burner operationthrough the detection of undesirable combustion products such as carbonmonoxide.

Still another object of this invention is to provide the improvedprotective means incorporating the aforementioned dual capabilities inthe form of a simple, reliable and inexpensive electronic circuit whichmay readily be applied in the most humble circumstances where suchprotection is so urgently needed.

The foregoing objects are achieved in the present invention by a simpleelectronic circuit which incorporates a phototransistor for thedetection of improper flame color, a carbon monoxide gas sensing elementand a solenoid actuator for the sounding of an alarm or for theinitiation of other protective action.

Further objects and advantages of the invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize this invention will be pointed out with particularity inthe claims annexed to and forming a part of this specification.

BRIEF DESCRIPTION OF THE DRAWING The present invention may be morereadily described by reference to the accompanying drawing in which:

FIG. 1 is a schematic representation of the detection and alarm circuit.

FIG. 2 is a schematic representation of a variation of the alarm portionof the circuit of FIG. 1.

FIG. 3 is an alternate embodiment of the flame color circuit included asa part of the circuit of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly tothe drawing by characters of reference, FIGS. 1 and 2 disclose adetection and alarm circuit 10 for use in monitoring the operation of agas burner, the circuit 10 comprising a direct current supply circuit11, a carbon monoxide detection circuit 12, a flame color sensingcircuit 13, and an alarm actuator circuit 14A or 148. The circuit 10 isconnected to an alternating current power source 9.

The direct current supply circuit 1 1 is a conventional half waverectifier circuit utilizing a step down transformer 15, a semiconductordiode l6 and a filter capacitor 17. Transformer 15 has a primary winding18 and a secondary winding 19 with a center tap 20. Transformer 15provides isolation and voltage step down between source 15 and circuit10, the source voltage 15 typically operating at volts, 60 hertz and thedesired secondary voltage being a low value preferably on the order of6.3 volts, each side of the center tap. Under these conditions a d-cvoltage of approximately 15 volts is provided across filter capacitor 17with a polarity as indicated by the positive and negative signs.

The carbon monoxide detection circuit 12 has as a key element a gasdetection element 22 which is obtainable from Figaro Engineering, Inc.of Toyonaka City, Osaka, Japan under the Figaro identification codeT.G.S. No. 202 or 303. Element 22 has an input resistive leg 23 and anoutput resistive leg 24. Leg 23 is physically separated from leg 24 by amedium, the resistance of which is normally high. In the presence ofcarbon monoxide, however, which penetrates the medium, the resistancebetween legs 23 and 24 is very significantly reduced so that currentflow between legs 23 and 24 is thereby greatly enhanced.

In addition to element 22, detection circuit 12 includes resistors and26, potentiometer 27 and semiconductor diode 28.

Input leg 23 of element 22 is serially connected with resistor 25 acrossthe upper half of secondary winding 19. An alternating current, i,, thusflows through leg 23 thereby heating element 22, the heat generatedcontributing to the operation of the element. By virtue of resistor 25,which has a relatively large value of resistance as compared with thatof input leg 23, the voltage potential of leg 23 is essentially that ofthe positive plate of capacitor 17.

Output leg 24 of element 22 has both ends connected to a common point 29which is tied by means of para]- lelly connected resistor 26 andpotentiometer 27 to the negative plate of capacitor 17. Under normalconditions essentially no current flows from secondary leg 24 throughresistor 26 and potentiometer 27. When carbon monoxide gas penetrateselement 22, however, a d-c current i flows from the positive plate ofcapacitor 17 to input leg 23, to output leg 24, through resistor 26 andpotentiometer 27 to the negative plate of capacitor 17. A positivevoltage thus developed at movable arm 29 of potentiometer 27 isdelivered via diode 28 to output terminal 30 of circuit 12, the positivevoltage at terminal 30 being indicative of an abnormally high level ofcarbon monoxide gas detected by circuit 12. Adjustment of potentiometer27 permits control of the detection level as appropriate for theapplication.

Flame color sensing circuit 13 includes as a key element aphoto-transistor 32. Transistor 32 has the operating characteristics ofa typical transistor in the sense that a positive current flowing frombase 33 to emitter 34 reduces the resistance of a positive current flowfrom collector 35 to emitter 34. In addition to such typical transistorcharacteristics, however, phototransistor 32 is fabricated in a mannerwhich permits exposure of the internal semiconductor element tosurrounding light. The design of transistor 32 is such that anincreasing level or whiteness of light striking the device produces areduced level of resistance, anode to cathode. The impinging light 36thus has a similar ef feet to or augments the effect of the base emittercurrent.

The wave lengths of the hues of the flame are sensed by thephoto-transistor. For example, if the phototransistor is set to monitora blue-green flame having the wave length of approximately 500 microns,any hue noted by the photo-transistor of a greater wave length willreduce its anode to cathode resistance. Since a white flame reflects allcolors and a progressively darker flame less color, the photo-transistoris sensitive to luminosity.

In addition to photo-transistor 32, circuit 13 includes a potentiometer37, resistors 38 and 39, capacitor and diode 42. Transistor 32 isserially connected, anode to cathode, with resistor 38 across the d-cvoltage appearing across filter capacitor 17.

During normal operation of the gas burner, the light strikingphoto-transistor 32 is not sufficient or of the proper wave length todrive transistor 32 into conduction so that a very low level of voltageexists across resistor 38. Under abnormal conditions, however, theimpinging light 36 causes transistor 32 to turn on thereby allowing arelatively large value of current to flow from collector 35 to emitter34 and through resistor 38. The voltage thus developed across resistor38 is coupled by means of serially connected resistor 39 and diode 42 tooutput terminal 43 and signals an abnormal flame color condition sensedby photo-transistor 32.

In an alternate embodiment 13A of circuit 13 as shown in FIG. 3, it maybe desired to rearrange the circuit 13 to permit thereby the detectionof a reduction in flame level as resulting from the total or partialextinction of the flame. In this case, the positions of the resistor 38and the transistor 32 with potentiometer 37 still connected betweencollector 35 and base 33 are reversed. Transistor 32 is in this casenormally conducting in the presence of normal burner operation and novoltage is coupled through resistor 39 and diode 42 to output terminal43. If the burner is totally or partially extinguished, however, apositive current flowing from the positive plate of capacitor 17 throughresistors 38 and 39 and diode 42 to output terminal 43 signals thefailure or improper operation of the burner.

In either embodiment of the circuits 13, 13A, the potentiometer 38connected between collector 35 and base 33 of transistor 32 provides ameans for biasing transistor 32 to render it sensitive to a desiredlightdetection level, a lower value of resistance set by potentiometer37 causing an increased bias current to flow from base 33 to emitter 34and thereby rendering the transistor 32 responsive to a lower level ofambient light. Capacitor 40 in conjunction with resistor 39 provides atime delay to prevent short bursts of light from producing an undesiredoutput signal at terminal 43.

Diodes 28 and 42 of circuits 12, 13 and 13A are coupling and blockingdiodes which isolate circuit 12 from circuit 13 or 13A and preventinteraction between these circuits.

Actuator circuit 14A includes two transistors 44 and 45 connected in thewell known Darlington configuration in series with solenoid coil 46across which is connected a recovery diode 47. A positive signal atoutput terminal 30 or 43 of circuit 12, 13 or 13A produces a positivebase emitter current in transistor 44 which in turn produces anamplified base emitter current in transistor 45. As a result, transistor45 saturates or exhibits a very low collector to emitter resistance sothat coil 46 is effectively connected across filter capacitor 17 throughtransistor 45 and is thereby energized to operate an alarm or a devicefor cutting of the gas supply.

At the termination of the signal from terminal 30 or 43, transistors 44and 45 revert to the off or high impedance state. Inductive energystored in coil 46 tends to sustain the current in coil 46 as transistors44 and 45 turn off and except for the presence of recovery diode 47, ahigh and possibly destructive voltage would appear as a consequenceacross transistors 44 and 45. Diode 47 provides a path for the sustainedcurrent to flow and allows the stored energy to be dissipated withoutthe generation of such a destructive voltage.

Under certain circumstances it may be desired that the alarm shouldcontinue to sound even after the undesired condition has ceased to existuntil the circuit is interrupted. The alternate alarm circuit 14B shownin FIG. 2 provides such a feature.

Circuit 14B incorporates a controlled rectifier 50, a transistor 51,resistors 52 and 53, a reset switch 54, a solenoid coil 55 and arecovery diode 56. A positive signal through diode 28 or 42 from circuitl2, 13 or 13A produces a base emitter current in transistor 51 whichrenders transistor 51 conductive between collector 57 and emitter 58. Aresulting current flowing through resistor 52 and transistor 51 flowsinto gate 59 of controlled rectifier 50. The gate current triggersrectifier 50 from an of! condition to an on" condition in whichrectifier 50 exhibits a very low value of resistance to current flowfrom anode 61 to cathode 62. With rectifier 50 in the on condition, coil55 is again effectively connected directly across capacitor 17 throughrectifier 50 and reset switch 54. By virtue of the typical operatingcharacteristics of controlled rectifier 50, the on condition ofrectifier 50 is sustained even after the disappearance of a positivesignal at diode 28 or 42 and after the termination of gate current intogate 59. The off condition of controlled rectifier 50 may be restored,however, by the momentary opening of reset switch 54.

A simple and versatile circuit has thus been shown in variousembodiments which permit the detection of carbon monoxide and thepresence or absence of desired or undesired light levels as produced bythe normal or abnormal operation of a gas burner flame or by a fireresulting from any cause. By virtue of its simplicity and its low cost,it may readily be applied in homes of modest means to reducesignificantly the hazard of bodily injury, death or property damage dueto fire or to the improper operation of gas burning equipment.

Although but a few embodiments of the present in vention have beenillustrated and described, it will be apparent to those skilled in theart thar various changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

What is claimed is:

l. A gas burner monitor comprising in combination:

a source of electrical energy having a pair of terminals,

a carbon monoxide detection circuit,

a flame color sensing circuit,

an alarm circuit,

said carbon monoxide detection circuit comprising a gas detectionelement connected to said source of electrical energy and producing afirst output signal when said detection circuit senses abnormal amountsof carbon monoxide around it,

said gas detection element comprising a resistance means which changesits electrical resistance when subjected to the presence of carbonmonoxide, said color sensing circuit comprising a phototransistor havingan anode, cathode and base, said base being connected through a variableresistance to one terminal of said source and said cathode beingconnected directly to said one terminal of said source, said emitterbeing connected through a resistance to the other terminal of saidsource, whereby exposure of said photo-transistor to a predeterminedlevel of light reduces the resistance of the phototransistor betweensaid anode and said cathode to change the base to emitter current flowthereby producing a second output signal, said variable resistancebiasing said phototransistor to render it sensitive to a desired lightdetection level, an alarm activating circuit, and means for connectingsaid first and second output signals to said alarm activating circuit toactuate an alarm. 2. The gas burner monitor set forth in claim 1wherein:

said resistance means reduces in resistance upon increase in wave lengthof the hue of the light sensed. 3. The gas burner monitor set forth inclaim 1 wherein:

said resistance means reduces in resistance upon increased whiteness ofthe flame. 4. The gas burner monitor set forth in claim 1 wherein:

said resistance means reduces in resistance upon increase in luminosityof the light sensed. 5. The gas burner monitor set forth in claim 1 infurther combination with: an alarm connected to said alarm circuit, andmeans connected to said alarm circuit for continuing its energizationafter the undesired condition determined by said detection circuit andsaid sensing circuit have ceased to exist and until said alarm circuit

1. A gas Burner monitor comprising in combination: a source ofelectrical energy having a pair of terminals, a carbon monoxidedetection circuit, a flame color sensing circuit, an alarm circuit, saidcarbon monoxide detection circuit comprising a gas detection elementconnected to said source of electrical energy and producing a firstoutput signal when said detection circuit senses abnormal amounts ofcarbon monoxide around it, said gas detection element comprising aresistance means which changes its electrical resistance when subjectedto the presence of carbon monoxide, said color sensing circuitcomprising a phototransistor having an anode, cathode and base, saidbase being connected through a variable resistance to one terminal ofsaid source and said cathode being connected directly to said oneterminal of said source, said emitter being connected through aresistance to the other terminal of said source, whereby exposure ofsaid photo-transistor to a predetermined level of light reduces theresistance of the phototransistor between said anode and said cathode tochange the base to emitter current flow thereby producing a secondoutput signal, said variable resistance biasing said phototransistor torender it sensitive to a desired light detection level, an alarmactivating circuit, and means for connecting said first and secondoutput signals to said alarm activating circuit to actuate an alarm. 2.The gas burner monitor set forth in claim 1 wherein: said resistancemeans reduces in resistance upon increase in wave length of the hue ofthe light sensed.
 3. The gas burner monitor set forth in claim 1wherein: said resistance means reduces in resistance upon increasedwhiteness of the flame.
 4. The gas burner monitor set forth in claim 1wherein: said resistance means reduces in resistance upon increase inluminosity of the light sensed.
 5. The gas burner monitor set forth inclaim 1 in further combination with: an alarm connected to said alarmcircuit, and means connected to said alarm circuit for continuing itsenergization after the undesired condition determined by said detectioncircuit and said sensing circuit have ceased to exist and until saidalarm circuit is interrupted.